(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of creating an improved layer of Anti Reflective Coating and therewith improved contact plugs for sub-micron devices.
(2) Description of the Prior Art
Continued decrease in the dimensions of semiconductor devices places more stringent requirements on the creation of sub-micron openings that are used to create contact plugs to the devices. Typically a layer of photoresist is used for the patterning and etching of layers of dielectric into which the contact plugs are created. Applying methods of photolithography involves reproducing an image, that is contained in an optical mask, in a layer of photoresist that is deposited over the surface of for instance a layer of dielectric. The optical mask is positioned between a radiation source of energy and the layer of photoresist. The image that is contained over the surface of the optical mask is transposed onto the underlying layer of photoresist by exposing the layer of photoresist through the optical mask. The pattern that is contained over the surface of the optical mask can be transparent to light with an opaque background or can inversely be an opaque pattern surrounded by a transparent background. By combining the light transmission characteristics of the optical mask with positive or negative reactive characteristics of the layer of photoresist, the layer of photoresist is converted by the photolithographic exposure to a readily removable substance resulting in reproducing the pattern that is contained over the surface of the optical mask in the layer of photoresist.
It is clear that the pattern of openings and trenches that is created in the layer of photoresist must meet very specific design requirements in order to create for instance satisfactorily performing interconnect lines or interconnect vias. This latter requirement results in the requirement that the exposure of the layer of photoresist must be uniform and must penetrate the layer of photoresist with equal energy throughout the height of the layer of photoresist. Uniformity of light penetration into and through the layer of photoresist does not allow for random reflection of light, since such a random reflection of light contributes to an arbitrary distribution of light energy throughout the region of exposure along the path of exposure. Light that penetrates a layer of photoresist will be reflected if this light penetrates through the layer of photoresist and encounters, after this penetration, a surface that reflects the light back in the approximate direction of the source of light energy. This approximate direction of light reflection is, among other factors, influenced by the planarity or topography of the reflecting surface and by the material that is contained in the reflecting surface. Further contributing to the negative impact that the reflected light has on the quality of the exposure is the fact that, in passing through a layer of photoresist, light energy will be absorbed, making the concentration or density of the reflected light dependent on the height of the layer of photoresist and having an effect throughout the height of the layer of photoresist that varies with the depth within the layer of photoresist. To avoid such complications, a conventional method is to assure that little or no light is reflected by an underlying surface, this is accomplished by using for the underlying surface a material that does not reflect light, commonly referred to as a layer of Anti Reflective Coating or ARC. Best results of suppression of reflection of photo-energy is obtained by using organic materials for the layer of ARC, examples of materials that can be used for anti reflective coatings include aluminum, silicon, titanium, zirconium, hafnium, chromium, and the like. The thickness of a layer of ARC is frequently not critical and can range between about 50 and 2,500 Angstrom. A layer of ARC can in addition be applied as an etch stop layer.
In a conventional processing flow, a layer of ARC is deposited over a supporting surface after which a pattern of trenches or openings is formed. Metal is deposited over the created openings and further processed for the creation of interconnect lines or contact plugs or contact vias. For many of the contact plugs that are created in order to interconnect devices, polysilicon is used as the preferred material for the contact plugs. For such applications, no problems are encountered in the deposition of a layer of ARC. The invention addresses concerns that are experienced for the creation of contact plugs of small critical dimensions where, using conventional processes, layers of ARC material will remain in place inside contact openings, resulting in imperfect contact openings.
U.S. Pat. No. 5,883,006 (Iba) reveals an opening process using BARL and Shipply resist.
U.S. Pat. No. 6,090,674 (Hsieh et al.) shows a method of forming a hole using an anti reflective coating.
U.S. Pat. No. 6,001,541 (Iyer) shows a method of forming a contact opening including an anti reflective coating.
A principle objective of the invention is to improve uniformity of the thickness of a layer of Anti Reflective Coating that is used for the creation of contact openings.
Another objective of the invention is to create a layer of Anti Reflective Coating that is uniform and that does not show irregular effects of cross section such as a hollow-shape or xe2x80x9cear-effectsxe2x80x9d.
Yet another objective of the invention is to create a layer of Anti Reflective Coating of uniform thickness over a supporting surface.
A still further objective of the invention is to create a layer of Anti Reflective Coating of reduced thickness over a supporting surface.
In accordance with the objectives of the invention a new processing sequence is provided for the creation of a layer of ARC. A first layer of ARC is deposited over a supporting surface, a blanket etch is performed to the surface of the first layer of ARC, leaving any openings that have been created in the supporting surface essentially filled with ARC material. A second layer of ARC is next applied over the surface of the etched first layer of ARC, this second layer of ARC provides a layer of ARC that is of uniform thickness over the supporting surface. Steps of baking may be applied to each of the layers of ARC after these layers have been deposited or after the first layer of ARC has been etched.